Magnetic element

ABSTRACT

A magnetic element is provided. The magnetic element includes a free magnetization layer having a surface area that is approximately 1,600 nm2 or less, the free magnetization layer including a magnetization state that is configured to be changed; an insulation layer coupled to the free magnetization layer, the insulation layer including a non-magnetic material; and a magnetization fixing layer coupled to the insulation layer opposite the free magnetization layer, the magnetization fixing layer including a fixed magnetization so as to be capable of serving as a reference of the free magnetization layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/458,470, filed Mar. 14, 2017, which is a continuation of U.S.application Ser. No. 15/290,408, filed Oct. 11, 2016, now U.S. Pat. No.9,634,239, which is a continuation of U.S. application Ser. No.15/049,418, filed Feb. 22, 2016, now U.S. Pat. No. 9,608,196, which is acontinuation of U.S. application Ser. No. 14/334,277, filed Jul. 17,2014, now U.S. Pat. No. 9,324,935, which is a continuation of U.S.application Ser. No. 13/560,708, filed Jul. 27, 2012, now U.S. Pat. No.8,879,315, which claims priority to Japanese Application No.2011-169867, filed Aug. 3, 2011, the disclosures of which areincorporated herein by reference.

BACKGROUND

The present disclosure relates to a storage element that includes astorage layer storing a magnetization state of a ferromagnetic layer asinformation and a magnetization fixing layer in which the direction ofmagnetization is fixed and the direction of the magnetization of thestorage layer is changed by causing a current to flow, and a storagedevice including the storage element.

With rapid development of various information apparatuses such as mobileterminals and large-capacity servers, new high performance features suchas high integration, high speed, and low power consumption have beenstudied on elements such as memories or logic circuits included invarious information apparatuses. In particular, semiconductornon-volatile memories have been highly advanced and flash memories suchas high-capacity file memories have been proliferated as hard diskdrives. On the other hand, development of ferroelectric random accessmemories (FeRAMs), magnetic random access memories (MRAMs), phase-changerandom access memories (PCRAMs), and the like is in progress to developthese memories to code storages or working memories and to substitutethe currently available NOR flash memories or DRAMs. Moreover, some ofthe memories have already been put to practical use.

Of the memories, MRAMs are capable of rewriting data rapidly and almostinfinitely (more than 10¹⁵ times) because data is stored according to adirection of magnetization of a magnetic body, and have already beenused in fields of industry automation, airplanes, or the like. MRAMs areexpected to be developed into code storages or working memories in thefuture in terms of a high speed operation and reliability. In reality,difficulties of low power consumption and large capacity have become aproblem. This problem is an inherent problem with a recording principleof MRAMs, that is, a method of causing a current to flow in two kinds ofaddress lines (a word line and a bit line) substantially perpendicularto one another and recording information by reversing the magnetizationof a magnetic layer of a magnetic storage element at an intersection ofthe address lines using a current magnetic field generated from eachaddress line, that is, reversing the magnetization using the currentmagnetic field generated from each address line.

As one of the solutions to this problem, recording types performedwithout dependency on the current magnetic field, that is, magnetizationreversing types, have been examined. Of these types, studies on spintorque magnetization reversal have actively been made (for example, seeJapanese Unexamined Patent Application Publication No. 2003-17782, U.S.Pat. No. 6,256,223, Japanese Unexamined Patent Application PublicationNo. 2008-227388, Phys. Rev. B 54, 9353 (1996), and J. Magn. Mat., 159,L1 (1996)).

The spin torque magnetization reversal type storage elements areconfigured by a magnetic tunnel junction (MTJ), as in MRAMs, in manycases. In such a configuration, a free magnetic layer is reversed when acurrent with a value equal to or greater than a given threshold iscaused to flow by applying a torque (which is called a spin transfertorque) to a magnetic layer when spin-polarized electrons passingthrough the magnetic layer fixed in a given direction enter another freemagnetic layer (in which a direction is not fixed). Rewriting “0/1” isperformed by changing the polarity of the current.

An absolute value of the current used to reverse the magnetic layer is 1mA or less in an element with a scale of about 0.1 μm. Further, scalingcan be performed to decrease the current value in proportion to anelement volume. Furthermore, there is an advantage of simplifying a cellstructure, since a recording current magnetic field generation wordline, which is necessary in MRAMs, is not necessary.

Hereinafter, an MRAM using spin torque magnetization reversal isreferred to as a spin torque-magnetic random access memory (ST-MRAM).The spin torque magnetization reversal is also referred to as spininjection magnetization reversal. An ST-RAM is highly expected to berealized as a non-volatile memory that has the advantages of low powerconsumption and large capacity in addition to the advantages of an MRAMin which data is rewritten rapidly and almost infinitely.

SUMMARY

In MRAMs, a writing line (a word line or a bit line) is providedseparately from a storage element and information is written (recorded)using a current magnetic field generated by causing a current to flow inthe writing line. Therefore, a sufficient amount of current necessaryfor writing the information can flow in the writing line.

On the other hand, in an ST-MRAM, it is necessary to reverse thedirection of the magnetization of the storage layer by performing thespin torque magnetization reversal by the current flowing in the storageelement. Since information is written (recorded) by causing a current toflow directly to the storage element, the storage device includes astorage element and a selection transistor connected to one another toselect a storage device writing information. In this case, the currentflowing in the storage element is restricted by the magnitude of thecurrent (the saturated current of the selection transistor) that canflow in the selection transistor.

Further, since an ST-MRAM is a non-voltage memory, it is necessary tostably store information written using the current. That is, it isnecessary to ensure stability (thermal stability) against thermalfluctuation of the magnetization of the storage layer.

When the thermal stability of the storage layer is not ensured, thereversed direction of the magnetization may be reversed again due toheat (temperature in an operation environment). Therefore, a writingerror may be caused.

In the storage element of the ST-MRAM, the advantage of the scaling,that is, the advantage of reducing the volume of the storage layer, canbe obtained compared to an MRAM according to the related art, asdescribed above.

However, when the volume of the storage layer is reduced, the thermalstability has a tendency to deteriorate under the same conditions of theother characteristics.

In general, when the volume of the storage element increases, thethermal stability and the writing current are known to increase.Conversely, when the volume of the storage element decreases, thethermal stability and the writing current are known to decrease.

It is desirable to provide a storage element capable of ensuring thermalstability as much as possible without an increase in a wiring currentand a storage device including the storage element.

According to an embodiment of the present disclosure, an informationstorage element comprises a first layer having a transverse length thatis approximately 45 nm or less and a volume that is approximately 2,390nm³ or less so as to be capable of storing information according to amagnetization state of a magnetic material, an insulation layer coupledto the first layer, the insulation layer including a non-magneticmaterial, and a second layer coupled to the insulation layer oppositethe first layer, the second layer including a fixed magnetization.

According to another embodiment of the present disclosure, aninformation storage element comprises a first layer capable of storinginformation according to a magnetization state of a magnetic material,an insulation layer coupled to the first layer, the insulation layerincluding MgO, and a second layer coupled to the insulation layeropposite the first layer, the second layer including a fixedmagnetization, and the insulation layer capable of allowing electronspassing through the second layer reach the first layer before theelectrons enter a non-polarized state.

Since the thermal stability of the storage layer can be sufficientlymaintained, the information recorded in the storage element can bestably held. Further, it is possible to miniaturize the storage device,improve reliability, and realize the low power consumption.

According to the embodiments of the present disclosure, the thermalstability can be efficiently improved for a writing current in anST-MRAM having vertical magnetic anisotropy. Therefore, it is possibleto realize the storage element ensuring the thermal stability as aninformation holding capability and thus having excellent characteristicbalance such as power consumption.

Thus, an operation error can be prevented and an operation margin of thestorage element can be sufficiently obtained.

Accordingly, it is possible to realize the memory operating stably andhaving high reliability.

Further, the writing current can be reduced, and thus the powerconsumption can be reduced when information is written on the storageelement. Accordingly, the entire power consumption of the storage devicecan be reduced.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram (perspective view) illustrating a storagedevice (memory device) according to an embodiment;

FIG. 2 is a sectional view illustrating the storage device according tothe embodiment;

FIG. 3 is a sectional view illustrating a storage element according tothe embodiment;

FIG. 4 is a diagram illustrating a cross-sectional configuration ofsamples of the storage element used in an experiment;

FIGS. 5A and 5B are diagrams illustrating dependencies of the size of astorage layer with respect to Ic and Δ obtained from an experiment ofSample 1;

FIG. 6 is a diagram illustrating a size dependency (indicated by ▴ inthe drawing) of the storage layer with respect to Δ obtained from theexperiment of Sample 1 and a size dependency (indicated by ♦ in thedrawing) of the storage layer with respect to Δ calculated based onsaturated magnetization Ms and an anisotropy magnetic field Hk obtainedthrough measurement of VSM;

FIGS. 7A and 7B are diagrams illustrating dependencies of the size of astorage layer with respect to Ic and Δ obtained from an experiment ofSample 2; and

FIG. 8 is a diagram illustrating a size dependency (indicated by ▴ inthe drawing) of the storage layer with respect to Δ obtained from theexperiment of Sample 2 and a size dependency (indicated by ♦ in thedrawing) of the storage layer with respect to Δ calculated based onsaturated magnetization Ms and an anisotropy magnetic field Hk obtainedthrough measurement of VSM.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Hereinafter, an embodiment of the present disclosure will be describedin the following order.

-   -   1. Storage Element according to Embodiment    -   2. Configuration of Storage Device according to Embodiment    -   3. Specific Configuration according to Embodiment    -   4. Experiment according to Embodiment

1. Storage Element According to Embodiment

First, a storage element according to an embodiment of the presentdisclosure will be described.

In the embodiment of the present disclosure, information is recorded byreversing the direction of magnetization of a storage layer of thestorage element through the above-described spin torque magnetizationreversal.

The storage layer is configured by a magnetic body including aferromagnetic layer and information is held according to a magnetizationstate (the direction of magnetization).

For example, a storage element 3 has a layer configuration shown in FIG.3. The storage element 3 includes at least a storage layer 17 and amagnetization fixing layer 15 as two ferromagnetic layers and includesan insulation layer 16 as an intermediate layer between the twoferromagnetic layers.

The storage element 3 further includes a cap layer 18 on the storagelayer 17 and includes an underlying layer 14 below the magnetizationfixing layer 15.

The storage layer 17 has magnetization perpendicular to a film surface.The direction of the magnetization is changed so as to correspond to theinformation.

The magnetization fixing layer 15 has magnetization perpendicular to afilm surface serving as a reference of the information stored in thestorage layer 17.

The insulation layer 16 is a non-magnetic body and is formed between thestorage layer 17 and the magnetization fixing layer 15.

When spin-polarized electrons are injected in a lamination direction ofthe layer configuration of the storage layer 17, the insulation layer16, and the magnetization fixing layer 15, the direction of themagnetization of the storage layer 17 is changed and information is thusrecorded on the storage layer 17.

Hereinafter, spin torque magnetization reversal will be describedsimply.

Electrons have two kinds of spin angular momenta. Here, the electronsare defined as upward electrons and downward electrons. In thenon-magnetic body, the upward and downward electrons are the same innumber. In the ferromagnetic body, the upward and downward electrons aredifferent in number. In the magnetization fixing layer 15 and thestorage layer 17, which are two ferromagnetic layers of the storageelement 3, a case in which electrons are moved from the magnetizationfixing layer 15 to the storage layer 17 when the directions of magneticmoments are opposite to one another will be considered.

The magnetization fixing layer 15 is a fixing magnetic layer in whichthe direction of a magnetic moment is fixed to ensure high coercivity.

In the electrons passing through the magnetization fixing layer 15, spinpolarization occurs, that is, there is a difference in number betweenthe upward and downward electrons. When the non-magnetic insulationlayer 16 has a sufficient thickness, the electrons reach the othermagnetic body, that is, the storage layer 17, before the spinpolarization of the electrons passing through the magnetization fixinglayer 15 is alleviated and the electrons enter a non-polarized state (inwhich the upward and downward electrons are the same in umber) in anormal non-magnetic body.

In the storage layer 17, since the sign of the degree of spinpolarization is opposite, some of the electrons are reversed, that is,the direction of the spin angular momentum is changed to lower theenergy of a system. At this time, since the entire angular momenta ofthe system have to be conserved, the reaction equivalent to the sum ofthe change in the angular momenta caused by the electrons of which thedirection is changed is applied to the magnetic moment of the storagelayer 17.

When a current, that is, the number of electrons passing in a unit time,is small, the total number of electrons of which the direction ischanged is also small. Therefore, a change in the angular momentumoccurring in the magnetic moment of the storage layer 17 is also small.However, when the current increases, the angular momentum can beconsiderably changed in a unit time.

A time change of an angular momentum is a torque. When a torque isgreater than a given threshold, the magnetic moment of the storage layer17 starts a precession movement. The magnetic moment is stabilized afterthe magnetic moment rotates by 180 degrees by uniaxial anisotropy. Thatis, the magnetic moment is reversed from an opposite direction to thesame direction.

When a current reversely flows in a direction in which electrons aresent from the storage layer 17 to the magnetization fixing layer 15 in astate of the same direction of the magnetization, a torque is applied ina case in which the electrons are reflected from the magnetizationfixing layer 15 and the spin-reversed electrons enter the storage layer17. Then, the magnetic moment can be reversed in the opposite direction.At this time, the amount of current necessary to cause the reversal isgreater compared to a case in which the magnetic moment is reversed fromthe opposite direction to the same direction.

It is difficult to intuitively understand the reversal of the magneticmoment from the same direction to the opposite direction, but thestorage layer 17 may be considered to be reversed to conserve the entireangular momenta of a system without the reversal of the magnetic momentsince the magnetization fixing layer 15 is fixed. Thus, “0/1” isrecorded by causing a current corresponding to each polarity and equalto or greater than a given threshold to flow in the direction from themagnetization fixing layer 15 to the storage layer 17 or in the oppositedirection.

Information is read using a magnetic resistive effect, as in an MRAMaccording to the related art. That is, a current flows in a directionperpendicular to a film surface, as in the recording case describedabove. The change phenomenon of electric resistance of an element isused depending on whether the direction of the magnetic moment of thestorage layer 17 is the same as or opposite to the direction of themagnetic moment of the magnetization fixing layer 15.

A metal or insulation material may be used as the material of theinsulation layer 16 formed between the magnetization fixing layer 15 andthe storage layer 17. When an insulation material is used as thematerial of the insulation layer 16, a high reading signal (resistancechange ratio) can be obtained and information can be recorded with alower current. In this case, an element is referred to as a magnetictunnel junction (MTJ) element.

When the direction of the magnetization of a magnetic layer is reversedthrough spin torque magnetization reversal, a threshold value Ic of anecessary current is different depending on whether a magnetization-easyaxis of the magnetic layer is in an in-plane direction or a verticaldirection.

The storage element according to the embodiment is a verticalmagnetization type storage element. A reversal current used to reversethe direction of the magnetization of the magnetic layer is assumed tobe Ic_para in an in-plane magnetization type storage element accordingto the related art.

When the magnetization is reversed from the same direction to theopposite direction (where the same direction and the opposite directionare the directions of the magnetization of the storage layer consideredusing the direction of the magnetization of the magnetization fixinglayer as a reference), “Ic_para=(A·α·Ms·V/g(0)/P)(Hk+2πMs)” issatisfied.

When the magnetization is reversed from the opposite direction to thesame direction), “Ic_para=−(A·α·Ms·V/g(π)/P)(Hk+2·Ms)” is satisfied(which is referred to as Equation (1)).

On the other hand, a reversal current of the vertical magnetization typestorage element is assumed to be Ic_perp. When the magnetization isreversed from the same direction to the opposite direction,“Ic_perp=(A·α·Ms·V/g(0)/P)(Hk−4πMs)” is satisfied.

When the magnetization is reversed from the opposite direction to thesame direction, “Ic_perp=−(A·α·Ms·V/g(π)/P)(Hk−4πMs)” is satisfied(which is referred to as Equation (2)).

In the equations, A denotes a constant, α denotes a damping constant, Msdenotes saturated magnetization, V denotes an element volume, P denotesspin polarizability, g(0) and g(π) denote coefficients corresponding toefficiency of a spin torque applied to a magnetic layer in the samedirection and the opposite direction, respectively, and Hk denotesmagnetic anisotropy (see Nature Materials., 5, 210 (2006)).

When the vertical magnetization type storage element (Hk−4πMs) iscompared to the in-plane magnetization type storage element (Hk+2πMs) inthe above-mentioned equations, the vertical magnetization type storageelement can be understood to be suitable by a low recording current.

In this embodiment, the storage element 3 is configured to include amagnetic layer (the storage layer 17) in which information can be heldaccording to a magnetization state and the magnetization fixing layer 15in which the direction of the magnetization is fixed.

To function as a storage device, written information has to be held. Thevalue of an index Δ (=KV/k_(B)T) of thermal stability is used as theindex of the capability of holding information. Here, Δ is expressed byEquation (3) below.

Δ=K·V/k _(B) ·T=Ms·V·Hk·(1/2K _(B) ·T)   Equation (3)

In this equation, Hk is an effective anisotropy field, k_(B) is theBoltzmann's constant, T is temperature, Ms is a saturated magnetizationamount, V is the volume of the storage layer 17, and K is anisotropicenergy.

The effective anisotropy field Hk receives the influence of magneticanisotropy such as shape magnetic anisotropy, induced magneticanisotropy, or crystal magnetic anisotropy. When a single-sectionsimultaneous rotation model is supposed, the effective anisotropy isequal to coercivity.

Further, when the threshold value Ic is expressed in relation to Δabove,

Equation (4) below is established.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{I_{C} = {\left( \frac{4{ek}_{B}T}{\hslash} \right)\left( \frac{\alpha \; \Delta}{\eta} \right)}} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

In this equation, e is an element charge, k_(B) is the Boltzmann'sconstant, T is temperature, Ms is a saturated magnetization amount, α isa Gilbert damping constant, H bar is the Flank's constant, and η is spininjection efficiency.

When the values of Hk, Ms, α, and η are determined according to Equation(3) and Equation (4), Δand Ic are proportional to the volume V of therecording layer. That is, when the volume V of the recording layerincreases, Δ and Ic increase. Conversely, when the volume V of thestorage layer decreases, Δ and Ic decrease. This principle can beunderstood from the above-mentioned theoretical equation.

However, in the actual storage layer, it has been found that anincreasing rate of Δ and Ic with respect to the volume of the storagelayer is changed when the volume of the storage layer is equal to orgreater than a given size.

According to this relation, when the volume of the storage layer isequal to or greater than the given size, only Ic increases without anincrease in Δ in spite of the fact that the volume of the storage layerincreases over the given size. This means that a ratio between Δ and Icdecreases when the volume of the storage layer is greater than a givensize of the storage layer. Therefore, it is difficult to establish aneffective existence condition of the ST-MRAM as a non-volatile memory,that is, compatibility between low-current information recording andhigh thermal stability of recorded information.

Accordingly, it is important to balance the value of the index Δ of thethermal stability and the threshold value Ic.

In many cases, the value of the index Δ of the thermal stability and thethreshold value Ic have a tradeoff relation. Therefore, thecompatibility is a task of maintaining the memory characteristics.

With regard to the threshold value of the current used to change themagnetization state of the storage layer 17, in fact, the thickness ofthe storage layer 17 is, for example, 2 nm. In a substantiallyelliptical TMR element with a planar pattern of 100 nm×150 nm, thethreshold value+Ic of a positive side is equal to +0.5 mA and thethreshold value−Ic of a negative side is equal to −0.3 mA. At this time,a current density is about 3.5×10⁶ A/cm². These values are identical tothose in Equation (1).

However, in a normal MRAM in which magnetization is reversed through acurrent magnetic field, a writing current of a few mA or more isnecessary.

Accordingly, in the ST-MRAM, the threshold value of the writing currentis sufficiently small, as described above. Therefore, the thresholdvalue can be understood to be effective for reducing the powerconsumption of an integrated circuit.

Further, since a wiring line necessary in the normal MRAM to generate acurrent magnetic field is not necessary, the advantage of the degree ofintegration can be obtained compared to the normal MRAM.

When the spin torque magnetization reversal is performed, information iswritten (recorded) by causing a current to flow directly to the storageelement 3. Therefore, the storage device includes the storage element 3and a selection transistor connected to each other to select the storageelement 3 that writes information.

In this case, the current flowing in the storage element 3 is restrictedby the magnitude of the current (the saturated current of the selectiontransistor) that can flow in the selection transistor.

The vertical magnetization type storage element is preferably used toreduce the recording current, as described above. Further, since avertical magnetization film can have magnetic anisotropy higher than anin-plane magnetization film, the large index Δ of the above-describedthermal stability is preferably maintained.

Examples of a magnetic material with vertical anisotropy include alloysof rare-earths and transition metals (TbCoFe and the like), metalmultilayer films (Cd/Pd multilayer films and the like), ordered alloys(FePt and the like), and materials using interfacial anisotropy (Co/MgOand the like) between an oxide and a magnetic metal. The alloys ofrare-earths and transition metals are not desirable as the material ofthe ST-MRAM. This is because vertical magnetic anisotropy is lost whenthe alloys are diffused and crystallized by heating. The metalmultilayer films are known to be diffused by heating and thusdeteriorate in the vertical magnetic anisotropy and the verticalmagnetic anisotropy is expressed when face-centered cubic (111)orientation is realized. Therefore, it is difficult to realize (001)orientation necessary in a high polarizability layer such as MgO or Fe,CoFe, CoFeB, or the like adjacent to MgO. Since L10 ordered alloys arestable at high temperatures and the vertical magnetic anisotropy isexpressed at the (001) orientation time, the above-mentioned problems donot occur. However, since it is necessary to arrange atoms orderly byperforming heating at the sufficiently high temperature of 500° C. ormore during manufacturing or by performing heating at the sufficientlyhigh temperature of 500° C. or more after the manufacturing, there is aprobability that undesirable diffusion may occur in another portion of alaminated layer such as a tunnel barrier or interface roughness mayincrease.

However, the above-mentioned problems rarely occur for a material usinginterface magnetic anisotropy, that is, a material in which a Co-basedmaterial or a Fe-based material is laminated on MgO serving as a tunnelbarrier. Therefore, the material is expected as the material of thestorage layer of the ST-MRAM.

In this embodiment, a material having Co—Fe—B as a base is used as thematerial of the storage layer 17. Several elements of Ti, V, Nb, Zr, Ta,Hf, Y, and the like may be added as non-magnetic metals to Co—Fe—B.

Further, in consideration of the saturated current value of theselection transistor, an MTJ element is configured using a tunnelinsulation layer that includes an insulator as the non-magneticinsulation layer 16 between the storage layer 17 and the magnetizationfixing layer 15.

When the MTJ element is configured using the tunnel insulation layer, amagnetoresistance ratio (MR ratio) can be increased compared to a casein which a grant magnetoresistive effect (GMR) element is configuredusing a non-magnetic conductive layer. Therefore, the intensity of areading signal can be increased.

In particular, the magnetoresistance ratio (MR ratio) can be increasedusing magnesium oxide (MgO) as the material of the insulation layer 16serving as a tunnel insulation layer.

In general, a spin transfer efficiency depends on the MR ratio. Thelarger the MR ratio is, the more the spin transfer efficiency isimproved. Therefore, a magnetization reversal current density can bereduced.

Accordingly, by using the magnesium oxide as the material of the tunnelinsulation layer and the storage layer 17, it is possible to reduce thethreshold value of the writing current through the spin torquemagnetization reversal. Therefore, information can be written (recorded)with a lower current. Further, the intensity of the reading signal canbe increased.

Thus, since the MR ratio (TMR ratio) can be ensured and the thresholdvalue of the writing current can be reduced through the spin torquemagnetization reversal, information can be written (recorded) with alower current. Further, the intensity of the reading signal can beincreased.

When the tunnel insulation layer is formed of a magnesium oxide (MgO)film, the MgO film is crystallized. Therefore, crystal orientation ismore preferably maintained in the 001 direction.

In this embodiment, the insulation layer 16 (the tunnel insulationlayer) formed between the storage layer 17 and the magnetization fixinglayer 15 is formed of not only magnesium oxide but also variousinsulators such as aluminum oxide, aluminum nitride, SiO₂, Bi₂O₃, MgF₂,CaF, SrTiO₂, AlLaO₃, and Al—N—O, a dielectric material, a semiconductor,or the like.

It is necessary to control the area resistive value of the insulationlayer 16 serving as the tunnel insulation layer such that the arearesistive value is equal to or less than about tens of Ωμm² in terms ofobtainment of the current density necessary for reversing the directionof the magnetization of the storage layer 17 through the spin torquemagnetization reversal.

In the tunnel insulation layer formed of a MgO film, the thickness ofthe MgO film should be set 1.5 nm or less, so that the area resistivevalue is in the above-described range.

In the ST-MRAM, 0 and 1 of information are determined by relative anglesof magnetization M17 of the storage layer 17 and magnetization M15 ofthe magnetization fixing layer 15.

The underlying layer 14 is formed below the magnetization fixing layer15 and the cap layer 18 is formed on the storage layer 17.

In this embodiment, the insulation layer 16 is formed as a magnesiumoxide layer to increase the magnetoresistance ratio (MR ratio).

By increasing the MR ratio, it is possible to improve the spin injectioneffect and reduce the current density necessary for reversing thedirection of the magnetization M17 of the storage layer 17.

The storage device shown in FIG. 1 and including the storage element 3shown in FIG. 2 has the advantage of applying a general semiconductorMOS forming process when a storage device is manufactured.

Accordingly, the storage device according to this embodiment isapplicable to a general-purpose memory.

Since the size of the storage layer 17 can be less than a size in whichthe direction of the magnetization is simultaneously changed, the powerconsumption can be suppressed to be as small as possible. Thus, it ispossible to realize the ST-MRAM using the thermal stability of thestorage element 3 as much as possible. The specific size of the storagelayer 17 of the storage element 3 is preferably equal to or less than adiameter of 45 nm.

Thus, it is possible to realize the storage element 3 that has excellentcharacteristic balance while ensuring the thermal stability as theinformation holding capability with low power consumption.

Since the operation margin of the storage element 3 can be sufficientlyobtained by removing an operation error, the storage element 3 canstably operate. Accordingly, it is possible to realize a storage deviceoperating stably and having high reliability.

Since the writing current is reduced, the power consumption can bereduced when information is written on the storage element 3.Accordingly, the entire power consumption of the storage device can bereduced.

In this embodiment, a metal such as Ta is used in the cap layer 18formed to be adjacent to the storage layer 17.

An element other than Co and Fe may be added to the storage layer 17according to the embodiment of the present disclosure.

When a different kind of element is added, it is possible to obtain aneffect of an improvement in heat resistance by diffusion prevention, anincrease in the magnetoresistive effect, an increase in a dielectricstrength voltage obtained with flattening, or the like. Examples of theadded element include B, C, N, O, F, Mg, Si, P, Ti, V, Cr, Mn, Ni, Cu,Ge, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, Ir, Pt, Au, Zr, Hf, Re, Os, or analloy thereof

In the configuration of the storage layer 17 according to the embodimentof the present disclosure, another ferromagnetic layer may be directlylaminated. Further, a ferromagnetic layer and a soft magnetic layer maybe laminated or a plurality of ferromagnetic layers may be laminatedwith a soft magnetic layer or a non-magnetic layer interposedtherebetween. Even when these magnetic layers are laminated, theadvantages of the embodiment of the present disclosure can be obtained.

In particular, when a plurality of ferromagnetic layers are laminatedwith a non-magnetic layer interposed therebetween, the strength of amutual interaction between the ferromagnetic layers can be adjusted.Therefore, it is possible to obtain the advantage of preventing themagnetization reversal current from increasing in spite of the fact thatthe dimension of the storage element 3 is equal to or less than asubmicron. In this case, Ru, Os, Re, Ir, Au, Ag, Cu, Al, Bi, Si, B, C,Cr, Ta, Pd, Pt, Zr, Hf, W, Mo, Nb, or an alloy thereof can be used asthe material of the non-magnetic layer.

In the magnetization fixing layer 15, the direction of the magnetizationis fixed only from the ferromagnetic layer or using antiferromagneticcoupling of an antiferromagnetic layer and a ferromagnetic layer.

The magnetization fixing layer 15 may include a single-layeredferromagnetic layer or may have a lamination ferri-pin structure inwhich a plurality of ferromagnetic layers are laminated with anon-magnetic layer interposed therebetween.

As the material of the ferromagnetic layer of the magnetization fixinglayer 15 having the lamination ferri-pin structure, Co, CoFe, CoFeB, orthe like can be used. As the material of the non-magnetic layer, Ru, Re,Ir, Os, or the like can be used.

As the material of the antiferromagnetic layer, a FeMn alloy, a PtMnalloy, a PtCrMn alloy, a NiMn alloy, an IrMn alloy, or a magnetic bodysuch as NiO, Fe₂O₃ can be used.

Further, a non-magnetic element such as Ag, Cu, Au, Al, Si, Bi, Ta, B,C, O, N, Pd, Pt, Zr, Hf, Ir, W, Mo, Nb, or the like may be added to themagnetic body to adjust the magnetic characteristics or adjust variousmatter properties such as a crystal structure, a crystalline property,and substance stability.

The remaining configuration other than the configuration of the storagelayer 17 and the magnetization fixing layer 15 of the storage element 3is the same as the configuration of the storage element 3 that recordsinformation through spin torque magnetization reversal according to therelated art.

In the configuration of the storage element 3, the storage layer 17 may,of course, be disposed below the magnetization fixing layer 15. In thiscase, the conductive oxide underlying layer undertakes the role of theconductive oxide cap layer.

As described above, the storage element 3 has the laminationconfiguration in which the cap layer 18, the storage layer 17, theinsulation layer 16, the magnetization fixing layer 15, and theunderlying layer 14 are laminated from the upper layer side. However,the storage element 3 of this embodiment may have a configuration inwhich the storage layer 17 is laminated below the magnetization fixinglayer 15.

Specifically, the storage element 3 may have a configuration in whichthe cap layer 18, the magnetization fixing layer 15, the insulationlayer 16, the storage layer 17, and the underlying layer 14 are formedsequentially from the upper layer side.

2. Configuration of Storage Device according to Embodiment

Next, the configuration of the storage device according to theembodiment of the present disclosure will be described.

FIGS. 1 and 2 are schematic diagrams illustrating the storage deviceaccording to the embodiment. FIG. 1 is a perspective view and FIG. 2 isa sectional view.

As shown in FIG. 1, the storage device according to the embodimentincludes the storage element 3 configured by an ST-RAM capable ofholding information by a magnetization state near an intersection of twokinds of addresses lines (for example, a word line and a bit line)perpendicular to one another.

That is, a drain region 8, a source region 7, and a gate electrode 1that form a selection transistor configured to select each storagedevice are formed in a portion isolated by element isolation layers 2 ofa semiconductor base substrate 10 such as a silicon substrate. Inparticular, the gate electrode 1 also serves as one address line (wordline) extending in the front and rear directions in the drawing.

The drain region 8 is formed commonly in the selection transistors onthe right and left of FIG. 1. A wiring line 9 is connected to the drainregion 8.

The storage element 3 that is disposed above the source region 7 andincludes the storage layer in which the direction of the magnetizationis reversed through the spin torque magnetization reversal is disposedbetween the source region 7 and the bit line 6 extending in the rightand left directions of FIG. 1. The storage element 3 is configured by,for example, an MTJ element.

As shown in FIG. 2, the storage element 3 includes two magnetic layers15 and 17. Of the two-layered magnetic layers 15 and 17, themagnetization fixing layer 15 is configured as a layer in which thedirection of magnetization M15 is fixed and the storage layer 17 isconfigured as a free magnetization layer in which the direction ofmagnetization M17 is changed.

The storage element 3 is connected to the bit line 6 and the sourceregion 7 with upper and lower contact layers 4 interposed therebetween,respectively.

Thus, when a current flows in the storage element 3 in the verticaldirection via two kinds of address lines 1 and 6, the direction of themagnetization M17 of the storage layer 17 can be reversed through thespin torque magnetization reversal.

In such a storage device, it is necessary to write information using acurrent equal to or less than a saturated current of the selectiontransistor. Therefore, the saturated current of the selection transistoris known to decrease with miniaturization of the storage device.Accordingly, to miniaturize the storage device, it is necessary toimprove the spin transfer efficiency and reduce the current flowing inthe storage device 3.

Further, to increase a reading signal, it is necessary to ensure a largemagnetoresistance ratio. Therefore, it is effective to use theabove-described MTJ structure, that is, the configuration of the storageelement 3 in which the insulation layer is formed as the tunnelinsulation layer (tunnel barrier layer) between the two layers of themagnetic layers 15 and 17.

When the tunnel insulation layer is used as the insulation layer, theamount of current flowing in the storage element 3 is restricted toprevent the insulation destruction of the tunnel insulation layer. Thatis, a current necessary for the spin torque magnetization reversalshould be suppressed to ensure the reliability of overwriting of thestorage element 3.

The current necessary for the spin torque magnetization reversal is alsoreferred to as a reversal current or a recording current.

Since the storage device is a non-volatile memory, the storage deviceshould stably store information written using a current. That is, it isnecessary to ensure stability (thermal stability) against thermalfluctuation of the magnetization of the storage layer.

When the thermal stability of the storage layer is not ensured, thereversed direction of the magnetization may be reversed again due toheat (the temperature of an operation environment) in some cases, andtherefore a writing error may be caused.

The storage element 3 of the storage device according to the embodimentof the present disclosure has the advantage of the scaling compared toan MRAM according to the related art, that is, the advantage of reducingthe volume of the storage element. However, when the volume of thestorage element is reduced, the thermal stability has a tendency todeteriorate under the same conditions of the other characteristics.

When the ST-MRAM has a large capacity, the volume of the storage element3 is further reduced. Therefore, to ensure the thermal stability is animportant task.

Accordingly, the thermal stability is a very important characteristic ofthe storage element 3 in the ST-MRAM. Even when the volume of thestorage element is reduced, the storage element should be designed toensure the thermal stability.

In the embodiment of the present disclosure, the size of the storagelayer 17 of the storage element 3 is less than a size in which thedirection of the magnetization is simultaneously changed. The specificsize of the storage layer 17 of the storage element 3 is preferablyequal to or less than a diameter of 45 nm. Thus, the power consumptionis suppressed to be as small as possible. Thus, it is possible torealize the ST-MRAM using the thermal stability of the storage element 3as much as possible.

The writing current for the storage element 3 is reduced. Since thepower consumption is reduced, the entire power consumption of thestorage device can be reduced.

The storage device shown in FIG. 1 and including the storage element 3shown in FIG. 2 has the advantage of applying a general semiconductorMOS forming process when the storage device is manufactured.

Accordingly, the storage device according to this embodiment isapplicable to a general-purpose memory.

3. Specific Configuration according to Embodiment

Next, a specific configuration of the embodiment of the presentdisclosure will be described.

In the configuration of the storage device, as described above withreference to FIG. 1, the storage element 3 capable of holdinginformation according to a magnetization state is disposed near anintersection of two kinds of address lines 1 and 6 (for example, a wordline and a bit line) perpendicular to each other.

Further, when a current flows in the storage element 3 in the verticaldirection via two kinds of address lines 1 and 6, the direction of themagnetization of the storage layer 17 can be reversed through the spintorque magnetization reversal.

FIG. 3 shows a detailed configuration of the storage element 3.

As shown in FIG. 3, the storage element 3 includes the magnetizationfixing layer 15 below the storage layer 17 in which the direction of themagnetization M17 is reversed through the spin torque magnetizationreversal.

In the ST-MRAM, 0 and 1 of information are determined by relative anglesof the magnetization M17 of the storage layer 17 and the magnetizationM15 of the magnetization fixing layer 15.

The insulation layer 16 configured as a tunnel barrier layer (tunnelinsulation layer) is disposed between the storage layer 17 and themagnetization fixing layer 15, so that the MTJ element is configured bythe storage layer 17 and the magnetization fixing layer 15.

The underlying layer 14 is formed below the magnetization fixing layer15.

The cap layer 18 is formed above the storage layer 17 (that is, the sideadjacent to the storage layer 17 and opposite to the insulation layer16).

In this embodiment, the storage layer 17 is a vertical magnetizationlayer formed of Co—Fe—B.

The cap layer 18 is formed of a conductive oxide.

The size of the storage layer 17 of the storage element 3 is less than asize in which the direction of the magnetization is simultaneouslychanged. The specific size of the storage layer 17 is preferably equalto or less than a diameter of 45 nm.

In this embodiment, when the insulation layer 16 is formed of amagnesium oxide layer, the magnetoresistance ratio (MR ratio) can beincreased.

By increasing the MR ratio, it is possible to improve the spin injectioneffect and reduce the current density necessary to reverse the directionof the magnetization M17 of the storage layer 17.

The storage element 3 according to this embodiment can be manufacturedby continuously forming the underlying layer 14 to the cap layer 18 in avacuum apparatus, and then forming the pattern of the storage element 3by etching or the like.

According to the above-described embodiment, since the storage layer 17of the storage element 3 is a vertical magnetization layer, it ispossible to reduce the amount of writing current necessary to reversethe direction of the magnetization M17 of the storage layer 17.

Thus, since the thermal stability can be sufficiently ensured as theinformation holding capability, the storage element 3 having theexcellent characteristic balance can be configured.

Since an operation error can be presented and the operation margin ofthe storage element 3 can be sufficiently obtained, the storage element3 can stably operate.

That is, the storage device operating stably and having high reliabilitycan be realized.

Further, since the wiring current is reduced, it is possible to reducethe power consumption when information is written on the storage element3.

As a result, the storage device including the storage element 3according to this embodiment can reduce the power consumption.

Thus, since a storage device having an excellent information holdingcharacteristic and operating stably and reliably can be realized, thepower consumption can be reduced in the storage device including thestorage element 3.

Further, the storage device shown in FIG. 1 and including the storageelement 3 shown in FIG. 3 has the advantage of applying a generalsemiconductor MOS forming process when the storage element ismanufactured.

Accordingly, the storage device according to this embodiment isapplicable to a general-purpose memory.

4. Experiment according to Embodiment

Here, samples of the storage element 3 were manufactured while changingthe size of the storage layer 17 in the configuration of the storageelement 3 described above with reference to FIGS. 1 to 3, and thecharacteristics of the storage element 3 were inspected.

In the actual storage device, as shown in FIG. 1, not only the storageelement 3 but also a switching semiconductor circuit and the like arepresent. However, an examination was made on a wafer on which only thestorage element 3 was formed to examine the magnetization reversalcharacteristic of the storage layer 17 adjacent to the cap layer 18.

A thermal oxide film with a thickness of 300 nm was formed on a siliconsubstrate with a thickness of 0.725 mm, and then the storage element 3having the configuration shown in FIGS. 3 and 4 was formed on thethermal oxide film.

Specifically, the material and the thickness of each layer of thestorage element 3 shown in FIG. 3 were as follows.

As shown in FIG. 4, the underlying layer 14 was formed as a laminationlayer of a Ta film with a thickness of 10 nm and a Ru film with athickness of 25 nm, the magnetization fixing layer 15 was formed as alayer including a CoPt film with a thickness of 2.0 nm, a Ru film with athickness of 0.8 nm, and a Co—Fe—B film with a thickness of 2.0 nm, theinsulation layer 16 was formed as a magnesium oxide layer with athickness of 0.9 nm, the storage layer 17 was formed as a CoFeB layer (Aof FIG. 4) or a CoFeB/Ta/CoFeB layer (B of FIG. 4) with a thickness of1.5 nm, and the cap layer 18 was formed as a layer including an oxidefilm with a thickness of 0.8 nm, a Ta film with a thickness of 3 nm, aRu film with a thickness of 3 nm, and a Ta film with a thickness of 3nm.

Here, the storage element 3 shown in A of FIG. 4 is indicated by Sample1 and the storage element 3 shown in B of FIG. 4 is indicated by Sample2.

In the film configuration, the composition of CoFeB of a ferromagneticlayer of the storage layer 17 was Co at 16%-Fe at 64%-B at 20%.

The insulation layer 16 configured by the magnesium oxide (MgO) film andthe oxide film of the cap layer 18 were formed by an RF magnetronsputtering method and the other films were formed by a DC magnetronsputtering method.

Each sample was subjected to heat processing in a heat processingfurnace in a magnetic field, after each layer was formed. Thereafter,the cylindrical storage layers 17 with diameters of 30 nm, 40 nm, 65 nm,75 nm, 90 nm, and 120 nm were manufactured by general electron beamlithography and a general ion milling process.

The characteristics of each sample of the manufactured storage element 3were evaluated as follows.

Before the measurement, a magnetic field was designed to be applied tothe storage element 3 to control the values of the reversal current suchthat the values of the reversal current in positive and negativedirections were symmetric.

The voltage to be applied to the storage element 3 was set up to 1 Vwithin a range in which the insulation layer 16 was not destructed.

Measurement of Saturated Magnetization Amount and Magnetic Anisotropy

The saturated magnetization Ms was measured through VSM measurementusing a vibrating sample magnetometer. Further, an anisotropy magneticfield Hk was measured by applying a magnetic field in a plane-verticaldirection and an in-plane direction and sweeping the magnetic field(measurement of a reversal current value and thermal stability).

The reversal current value was measured to evaluate the writingcharacteristic of the storage element 3 according to this embodiment.

The resistive value of the storage element 3 was then measured bycausing a current with a pulse width in the range of 10 μs to 100 ms toflow in the storage element 3.

Further, the value of the current for which the direction of themagnetization M17 of the storage layer 17 of the storage element 3 wasreversed was calculated by changing the amount of current flowing in thestorage element 3. A value obtained by extrapolating the pulse widthdependency of the value of the current at a pulse width of 1 ns was setas the value of the reversal current.

The inclination of the pulse width dependency of the value of thereversal current corresponds to the index Δ of the above-describedthermal stability of the storage element 3. As the value of the reversalcurrent is changed less by the pulse width (the inclination is small),the thermal stability means the strong degree against heat disturbance.

In consideration of a variation in the storage element 3, twenty storageelements 3 with the same configuration were manufactured to carry outthe above-described measurements, and the average values of the valuesof the reversal current and the indexes Δ of the thermal stability werecalculated.

A reversal current density Jc0 was calculated from the average value ofthe values of the reversal current obtained through the measurement andthe area of the plane pattern of the storage element 3.

Here, FIGS. 5A and 5B show the size dependency of the storage layer 17of the storage element 3 with respect to Ic (FIG. 5A) and Δ (FIG. 5B)obtained for Sample 1 from the experiment. In FIG. 5A, it can beconfirmed that Ic increases as the size of the storage layer 17increases, as anticipated from the equation of Ic perp. Conversely, asshown in FIG. 5B, does not coincide with the relation shown in Equation3. Further, Δ does not monotonically increase, even when the size of thestorage element increases.

To inspect the relation between Δ and the size of the storage layer 17in more detail, the saturated magnetization Ms (=760 emu/cc) and theanisotropy magnetic field Hk (=2 kOe) were first inspected using VSM,and then Δ expected from the values of the matter properties wascalculated using the saturated magnetization Ms, the anisotropy magneticfield Hk, and Equation 3. FIG. 6 shows a size dependency (indicated by ▴in the drawing) of the storage layer 17 with respect to Δ obtained fromthe experiment of Sample 1 and a size dependency (indicated by ♦ in thedrawing) of the storage layer 17 with respect to Δ calculated based onthe saturated magnetization Ms and the anisotropy magnetic field Hkobtained through the measurement of VSM. From FIG. 6, it can beunderstood that the calculation result and the experiment resultcoincide with each other up to about 40 nm which is the diameter of thestorage layer 17, but the calculation result and the experiment resultare increasingly different from each other in the element size equal toor greater than 40 nm. In general, when a magnetic body is small,uniform (simultaneous) magnetization rotation occurs. When a magneticbody is large, uneven magnetization rotation easily occurs.

The reason why the calculation result and the experiment result aredifferent from one another is considered to be that the state of thematter property is changed when the magnetization of the storage layer17 is reversed from the diameter of about 40 nm. That is, when the sizeof the storage layer is equal to or less than the diameter of about 40nm, the magnetization of the storage layer 17 is considered to besimultaneously rotated.

When the size of the storage layer is greater than the diameter of about40 nm, it is considered that the magnetization of partial portions inwhich rotation is easy in the storage layer 17 is initially reversed andthe magnetization of the remaining portions is thus reversed due to theinfluence of the initial magnetization. In other words, themagnetization is considered to be unevenly rotated.

When Δ is regarded to be almost uniform in the storage layer 17 of whichthe size is equal to or greater than the diameter of 40 nm, the elementsize in which Δ obtained by the calculation coincides with Δ obtained bythe experiment can be known to be 45 nm from the graph of an equation of“y=19697x+17.634.” This value can be considered as a value for making Icas small as possible while Δ is ensured to be as large as possible. Thatis, the size of the storage layer 17 can be understood to be thediameter of 45 nm. The size of the storage layer can be converted to avolume of “1.5 nm×πx(45/2)²=2390 nm³.”

In the storage element 3 with a size equal to or less than the diameterof 45 nm, the good balance of Δ and Ic can be said to be maintained, asexpected from the calculation result, since Δ and Ic are lessened.

Accordingly, when the storage element 3 indicated by Sample 1 is formedsuch that the size of the storage layer 17 is equal to or less than thecritical size in which the direction of the magnetization issimultaneously changed, that is, the size of the storage layer 17 isequal to or less than the diameter of 45 nm, the power consumption canbe suppressed to be as small as possible. Thus, it is possible torealize the ST-MRAM using the thermal stability of the storage element 3as much as possible.

Likewise, FIGS. 7A and 7B show the size dependency of the storage layer17 with respect to Ic (FIG. 7A) and Δ (FIG. 7B) obtained for Sample 2from an experiment. FIG. 8 shows a size dependency (indicated by ▴ inthe drawing) of the storage layer 17 with respect to obtained from theexperiment of Sample 2 and a size dependency (indicated by ♦ in thedrawing) of the storage layer 17 with respect to Δ calculated based onthe saturated magnetization Ms and the anisotropy magnetic field Hkobtained through the measurement of VSM. In Sample 2, the saturatedmagnetization Ms was 650 emu/cc and the anisotropy magnetic field Hk was2.15 kOe. In Sample 2 shown in FIGS. 7A, 7B, and 8, when the size isequal to or less than the diameter of 45 nm as in Sample 1, the powerconsumption can be suppressed to be as small as possible. Thus, it ispossible to realize the ST-MRAM using the thermal stability of thestorage element 3 as much as possible.

When the storage layer 17 is formed of Co—Fe—B or a material in which anon-magnetic material is added to Co—Fe—B and the size of the storagelayer 17 is equal to or less than the critical size in which thedirection of the magnetization is simultaneously changed, that is, thediameter of 45 nm, as described above, the power consumption can besuppressed to be as small as possible. Thus, it is possible to realizethe ST-MRAM using the thermal stability of the storage element 3 as muchas possible.

The embodiment has been described, but the present disclosure is notlimited to the layer configuration of the storage element 3 according tothe above-described embodiment. Various layer configurations can berealized.

For example, in the above-described embodiment, the compositions ofCo—Fe—B of the storage layer 17 and the magnetization fixing layer 15are the same as each other. The present disclosure is not limited to theabove-described embodiment, but may be modified in various ways withinthe scope not departing from the gist of the present disclosure.

The underlying layer 14 or the cap layer 18 may be formed of a singlematerial or may have a lamination configuration of a plurality ofmaterials.

The magnetization fixing layer 15 may be configured by a single layer ora lamination ferri-pin structure of two layers of a ferromagnetic layerand a non-magnetic layer. Further, an antiferromagnetic layer may beadded to a layer with the lamination ferri-pin structure.

Additionally, the technology of the present disclosure may also adoptconfigurations as below.

-   (1) A storage element including:    -   a storage layer that holds information according to a        magnetization state of a magnetic body;    -   a magnetization fixing layer that has magnetization serving as a        reference of the information stored in the storage layer; and    -   an insulation layer that is formed of a non-magnetic body        disposed between the storage layer and the magnetization fixing        layer,    -   wherein the information is stored by reversing the magnetization        of the storage layer using spin torque magnetization reversal        occurring with a current flowing in a lamination direction of a        layer configuration of the storage layer, the insulation layer,        and the magnetization fixing layer, and    -   a size of the storage layer is less than a size in which a        direction of the magnetization is simultaneously changed.-   (2) The storage element according to (1), wherein a ferromagnetic    material of the storage layer is Co—Fe—B.-   (3) The storage element according to (1), wherein a non-magnetic    material is added to Co—Fe—B of the ferromagnetic material of the    storage layer.-   (4) The storage element according to (1), (2), or (3), wherein the    storage layer and the magnetization fixing layer have magnetization    perpendicular to a film surface.-   (5) The storage element according to (1), (2), or (3), wherein a    diameter of the storage layer is less than 45 nm.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A magnetic element comprising: afree magnetization layer having a transverse length that isapproximately 45 nm or less, the free magnetization layer including amagnetization state that is configured to be changed; an insulationlayer coupled to the free magnetization layer, the insulation layerincluding a non-magnetic material; and a magnetization fixing layerdirectly coupled to the insulation layer opposite the free magnetizationlayer, the magnetization fixing layer including a fixed magnetization.2. The magnetic element of claim 1, wherein the non-magnetic materialincludes MgO.
 3. The magnetic element of claim 1, wherein a size of thefree magnetization layer is equal or less than a size in which adirection of the magnetization is simultaneously changed.
 4. Themagnetic element of claim 1, wherein the free magnetization layerincludes a first ferromagnetic material.
 5. The magnetic element ofclaim 4, wherein the first ferromagnetic material includes Co, Fe, andB.
 6. The magnetic element of claim 5, wherein the free magnetizationlayer includes a single layer of the first ferromagnetic material. 7.The magnetic element of claim 6, wherein the single layer of the firstferromagnetic material has a thickness of approximately 1.5 nm.
 8. Themagnetic element of claim 5, wherein the free magnetization layerincludes a plurality of layers of the first ferromagnetic material. 9.The magnetic element of claim 8, wherein at least one of the pluralitylayers of the first ferromagnetic material has a thickness of less than1.5 nm.
 10. The magnetic element of claim 5, further comprising a caplayer coupled to the free magnetization layer opposite the insulationlayer.
 11. The magnetic element of claim 10, wherein the cap layerincludes a Ru layer.
 12. The magnetic element of claim 11, wherein thecap layer further includes a Ta layer.
 13. The magnetic element of claim12, wherein the Ru layer is between the Ta layer and the freemagnetization layer.
 14. The magnetic element of claim 13, wherein themagnetization fixing layer includes a second ferromagnetic material. 15.The magnetic element of claim 14, wherein the second ferromagneticmaterial includes Co and Fe.
 16. The magnetic element of claim 15,wherein the magnetization fixing layer includes Ru.
 17. The magneticelement of claim 16, wherein the magnetization fixing layer includes afirst layer including Co and Fe, a second layer including Ru, and athird layer including Co, and wherein the second layer is between thefirst layer and the third layer.
 18. The magnetic element of claim 17,further comprising an underlying layer including Ru, and wherein themagnetization fixing layer is between the underlying layer and theinsulation layer.
 19. The magnetic element of claim 1, wherein the freemagnetization layer has a transverse length that is approximately 40 nmor less.
 20. The magnetic element of claim 1, wherein the freemagnetization layer has a transverse length that is approximately 30 nmor less.
 21. The magnetic element of claim 1, wherein the freemagnetization layer has a volume that is approximately 2,390 nm³ orless.
 22. The magnetic element of claim 1, wherein the freemagnetization layer has a volume that is approximately 1,950 nm³ orless.
 23. A storage device comprising a magnetic element as recited inclaim 1.